I wouldn't rule out vacuum leaks. Get out the carb cleaner and spray it around the base of the carb/throttle body and at the intake manifold gasket areas. Some prefer to use propane for this test. I like to take the air cleaner off and cup my hands over the air intake. If as I progressively choke off the airflow the idle normalizes, a vacuum leak is indicated.

The idle air control motor could be stuck or the passage could be contaminated. To check, pull the air cleaner assy off, and look at the passenger rear of the throttle body. You'll see a 4-wire square plug sticking out at a 45 degree angle, and a hole inside the throat of the body in that corner. If you plug that hole with your finger, the truck should die. If not, a vacuum leak is your issue.

I was wondering where the IAC valve is on these throttle bodies. I will check when I get home. The contamination might be possible becuase I had the air cleaner off while the truck was sitting before this high-idle started.